In recent years, oil and energy shortages cause the rising oil prices. Moreover, since the global warming phenomenon does not relieve, the reduction of carbon emissions is the policy of the governments around the world. However, since most of the today's large vehicles use oil as the power source, the exhausted waste gas causes the air pollution problems. Although a small portion of large vehicles uses batteries as the power source, the use of electricity as the power source has many difficulties to be overcome. For example, it is critical to balance the stored energy of plural batteries in order to avoid the over-discharging problem. As known, the over-discharging problem may shorten the use life of the battery.
Moreover, because of the demands on power and endurance, the large electric vehicle uses a great number of battery modules in serial connection and parallel connection so as to acquire high voltage and high current. In case that the battery modules are connected with each other in series, the battery modules have the same discharging current. That is, the serially-connected battery modules in a battery box usually have matched electric properties. Consequently, the discharging conditions of these battery modules are very similar. If the electric properties of these battery modules do not match each other, the electric energy of some of the battery modules is possibly exhausted, and the exhausted battery modules are possibly damaged because of the over-discharging problem. However, the process of allowing the electric properties of the serially-connected battery modules in the battery box to match each other is time-consuming and costly. Since the fabricating process of the battery module is largely prolonged and the product price is increased, the competitiveness of the product is impaired.
In case that the power structure of the electric vehicle comprises plural batteries in parallel connection, the power structure can normally work when one battery is damaged. However, since different battery modules have different electric properties, the electric energy of some of the battery modules is exhausted earlier. The exhausted battery modules enter a low voltage protection state. Under this circumstance, the output current of the power structure is reduced and the endurance of the electric vehicle is obviously lowered.
Therefore, there is a need of providing a power structure of a large electric vehicle and a control method thereof in order to overcome the above drawbacks.